The invention relates to a method for controlling the functions of an electronic driving stability program for a motor vehicle according to the preamble of patent claim 1.
German patent applications DE 199 36 439 A1 and DE 100 34 723 A1 disclose that an electronic driving stability program (ESP) which is effective in a motor vehicle can ensure that the driver maintains control over his motor vehicle if the latter threatens to leave its lane due to pronounced steering movements, pronounced deceleration of the vehicle and/or adverse weather conditions. To do this, an ESP computer uses sensors and this driving stability program to monitor the driving state of the motor vehicle and the steering behavior of the driver. By selectively activating the service brake at individual wheels of the vehicle and, if appropriate, reducing the power of the engine, the driving stability program stabilizes the motor vehicle and thus avoids uncontrolled movements of the vehicle.
In addition it is known that vehicles which are equipped with such a driving stability program generally have an electrical switch whose activation allows the driving stability program to be activated or deactivated. In the case of snow and ice on the road, for example, it may be appropriate to prevent the control intervention by such a driving stability program. In particular when the properties of the underlying surface change the driver of the vehicle is required to activate or deactivate the driving stability program in a way which is appropriate for the driving situation.
Furthermore, in the winter mode of the vehicle with an electronic driving stability program what is referred to as a snow wedge may build up between the underlying surface and the bottom of the vehicle or the vehicle wheels. Such a snow wedge is produced, for example, as a result of snow being pushed together essentially in parallel with the underlying surface or as a result of the vehicle wheels sinking into a comparatively deep layer of snow and compacting the snow. At the same time, wedges can also be produced from other roadway materials such as sand, grit stones, branches, etc. The wedge of roadway material may affect one wheel of the vehicle or a corner of the vehicle or an axle of the vehicle or the entire front or rear side of the vehicle.
A disadvantage with respect to the method of functioning of an electronic driving stability program in such a driving situation is the fact that a vehicle wheel which is affected by the wedge of roadway material may be braked and may thus only transmit reduced driving torque, or even no driving torque at all, to the underlying surface in a way which is effective in terms of drive. This state is detected by the driving stability program so that the latter acts, for example, on the axially opposite vehicle wheel by selective brake intervention and reduces the ability of said wheel to transmit torque to the carriageway in such a way that a rotational movement of the vehicle about its vertical axis does not occur.
At a low initial speed of the vehicle, this can ultimately lead to the vehicle coming to a standstill, and when the driving stability program is switched on it is not possible for the driver to “cut through” the respective wedge of roadway material, or move it away in some other way, with spinning vehicle wheels, for example.
Furthermore, driving of a vehicle with a ride level control system onto a wedge of roadway material can lead to said system causing one side of the bodywork of the vehicle to be lowered or raised as a result of the wedge in order to compensate for the oblique position which is sensed, as a result of which the bottom side of the floor of the vehicle comes to rest on the wedge of roadway material over a large area or the affected front side or rear side of the vehicle is raised in its entirety in order to equalize the level.
In order to avoid the aforesaid disadvantages, the object of the invention is to propose a method for controlling the functions of an electronic driving stability program with which it is ensured that a motor vehicle will operate in a way which is compatible for the driving situation even when a wedge of roadway material is formed in front of the wheels of the vehicle or between the floor of the vehicle and the underlying surface.